Male-biased sex ratio increases female egg laying and fitness in the housefly, Musca domestica
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A biased operational sex ratio (OSR) can have multiple, confounding effects on reproductive fitness. A biased OSR can increase harassment and mating activity directed towards potential mates but may also increase the ability of potential mates to choose a good partner if lower quality mates are screened out through competitive interactions. Additionally, a biased OSR may affect reproductive fitness through changes in male ejaculate content or in female reproductive response. We quantified how a male-biased OSR (1:1, 2:1, or 5:1 male to female) affected the size of a female’s first egg clutch and her offspring’s survivorship in the housefly, Musca domestica. A male-biased OSR increased female fitness: females laid more eggs in their first clutch, had increased offspring survivorship at a 2:1 versus 1:1 OSR, and had equivalent fitness with a 5:1 male to female OSR. Courtship activity increased when the OSR was male-biased but was not a significant predictor of female fitness. Trials where females chose their mates versus trials where a random male was chosen for them had equivalent first clutch sizes and offspring survivorship. These results suggest that there are cryptic effects from a male-biased OSR on female fitness that are most likely driven by pre-copulatory social environment.
KeywordsCompetition Courtship Sex ratio OSR Sexual conflict Indirect effects Clutch size
J.A.C. received support from an Alliance for Graduate Education and the Professoriate Research Fellowship (National Science Foundation Cooperative Agreement HRD-0450363), the Ford Foundation, and a National Science Foundation pre-doctoral fellowship. This work was supported by National Science Foundation DEB-0128855 to L.M. We would like to thank four anonymous reviewers for their insightful comments. All experiments complied with the current laws of the country in which they were performed.
Conflict of interest
The authors declare that they have no conflict of interest.
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